The term “STROKE” is used to describe a medical event whereby blood supply to the brain or specific areas of the brain is restricted or blocked to the extent that the supply is inadequate to provide the required flow of oxygenated blood to maintain function. The brain will be impaired either temporarily or permanently, with the patient experiencing a loss of function such as sight, speech or control of limbs. There are two distinct types of stroke, hemorrhagic and embolic. Embolic stroke may be caused by embolic material that may become dislodged after stenting.
Medical literature describes artery disease as a significant source of embolic material. Typically, an atherosclerotic plaque builds up in the arteries. The nature of the plaque varies considerably, but in a significant number of cases pieces of the plaque can break away and flow distally and, for example, block blood flow to specific areas of the brain and cause neurological impairment, plaque can also break free and flow into the lungs or heart and cause other adverse events. Treatment of the disease in the carotid artery is classically by way of surgical carotid endarterectomy whereby, the carotid artery is cut and the plaque is physically removed from the vessel. The procedure has broad acceptance with neurological complication rates quoted as being low, somewhere in the order of 5% although claims vary widely on this.
Not all patients are candidates for surgery. A number of reasons may exist such that the patients could not tolerate surgical intervention. In these cases and in an increasing number of candidates that are surgical candidates are being treated using transcatheter techniques. In this case, the evolving approach uses devices inserted in the femoral artery and manipulated to the site of the stenosis. A balloon angioplasty catheter is inflated to open the artery and an intravascular stent is sometimes deployed at the site of the stenosis. The action of these devices as with surgery can dislodge embolic material which will flow with the arterial blood and if large enough, eventually block a blood vessel and cause a stroke.
It is known to permanently implant a filter in human vasculature, such as the vena cava, to catch embolic material. It is also known to use a removable filter for this purpose. Such removable filters typically comprise umbrella type filters comprising a filter membrane supported on a collapsible frame on a guidewire for movement of the filter membrane between a collapsed position against the guidewire and a laterally extending position occluding a vessel. Examples of such filters are shown in U.S. Pat. No. 4,723,549, U.S. Pat. No. 5,053,008, U.S. Pat. No. 5,108,419 and WO 98/33443. Various deployment and/or collapsing arrangements are provided for the umbrella filter.
Improved filter devices have been designed to overcome the shortcomings of the previous filters. For example, in one embodiment, the filter is freely disposed along the length to the guidewire, thereby allowing the guidewire to be moved independently of the filter assembly.
After the filter has crossed the stenosed region of the vessel, the filter is deployed within the vessel to capture any emboli that may be dislodged during subsequent medical procedure(s).
One example of a subsequent medical procedure that may be performed is percutaneous transluminal coronary angioplasty (PTCA). PTCA is a procedure for treating vascular disease. This procedure generally entails introducing a balloon catheter assembly into the vascular system of a patient via the brachial or femoral artery and advancing the balloon catheter assembly through the vasculature until the balloon is positioned across an occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress against the plaque of the lesion to remodel the vessel wall. Subsequently, the balloon is deflated to allow the balloon catheter assembly to be withdrawn from the vasculature.
Typically after PTCA, a stent may be in the lumen to maintain the vascular patency. Additionally, to better effectuate the treatment of such vascular disease, it may be preferable to load an intraluminal device or prosthesis with one or more beneficial agents, such as antiproliferatives, for delivery to a lumen. One commonly applied technique for the local delivery of a drug is the use of a polymeric carrier coated onto the surface of a stent. Such conventional methods and products generally have been considered satisfactory for their intended purpose.
The stent may be constructed to be a self-expanding stent, whereby the stent expands to support the vessel when a restraining sheath is removed or a balloon expanadable stent, which is expanded by inflating a balloon on which the stent is mounted or crimped around. In either instance, stents are constructed having multiple struts creating scaffolding for the vessel. While the struts of the stent support the vessel, the open areas between the struts do not support the vessel or the plaque. In many instances plaque extrudes between the struts in to the open areas of the stent, the extruded plaque may eventually break free and form emboli within the vessel which may cause a stroke.
Therefore, there is a need for a device and method of use for reducing emboli due to this extruded plaque.